(a) Field of the Invention
The present invention relates to a color filter for a liquid crystal display, and more particularly to a color filter for a liquid crystal display capable of offering a wide view angle by dividing a pixel area into a number of smaller domains.
(b) Description of the Related Art
Generally, a liquid crystal display is a device in which liquid crystal material is injected between an upper substrate on which common electrodes and color filters, etc. are formed, and a lower substrate on which a thin film transistor and pixel electrodes, etc. are formed. Different electric potentials are applied to the pixel electrodes and the common electrodes to form an electric field to change arrangement of liquid crystal molecules, thereby controlling transmissivity of light to embody images.
The biggest problem of a liquid crystal display is that it has a narrow view angle. There have been many approaches to enlarging the view angle. Among them, the method of aligning liquid crystal molecules perpendicularly to the upper and the lower substrates and forming an opening pattern or protrusions on the pixel electrodes or the common electrodes looks promising.
In such an opening-pattern forming method, an opening pattern is formed on each of the pixel electrodes and the common electrodes, and orientations of the liquid crystal molecules are arranged using the fringe field caused by the opening patterns to obtain a wide view angle. With this method, it is a key point to obtain uniform opening patterns.
In the opening pattern method of a transparent electrode such as ITO, IZO etc., a transparent overcoating film is formed on a colored film and the transparent electrode is vacuum-deposited on it. Adhesion of the transparent electrode to the overcoating film is a very important factor that determines the degree and quality of the opening pattern formation.
Currently, acrylic epoxy materials are typically used as the transparent overcoating film. However, acrylic epoxy materials have problems such as decreased heat resistance due to the transparent electrode annealing, poor adhesion to the Cr black matrix (BM), and poor light resistance due to UV cleaning which is performed to improve adhesion of the transparent electrode. Accordingly, there is a need for the development of a new material.
An object of the present invention is to provide a color filter for a liquid crystal display having a transparent overcoating film with a wide a transparent electrode such as ITO, IZO etc. pattern formation margin, and good heat resistance, light resistance, and transmissivity.
It is another object of the present invention to provide a color filter for a liquid crystal display that can offer a wide view angle to a liquid crystal display, preferably a transparent electrode PVA mode liquid crystal display.
It is another object of the present invention to provide a liquid crystal display, preferably a transparent electrode PVA mode liquid crystal display that contains such a color filter.
In order to achieve these objects, the present invention provides a color filter for a liquid crystal display comprising a pixel area, a black matrix, and a transparent overcoating film, wherein the transparent overcoating film comprises a thermosetting polymer obtained by mixing:
a) polyamic acid having siloxane terminal groups; and
b) an epoxy compound having 1 to 4 epoxy groups.
Preferably, the polyamic acid of a) and the epoxy compound of b) are mixed in the weight ratio ranging from about 3:1 to about 3:2.
The present invention also provides a liquid crystal display that contains such a color filter. In one preferred embodiment, this liquid crystal display is a PVA liquid crystal display comprising:
a first insulating substrate;
first wiring formed on the first insulating substrate;
second wiring also formed on the first insulating substrate and intersecting the first wiring;
pixel electrodes formed on each pixel area defined by the intersection of the first wiring and the second wiring and having a first opening pattern; and
a thin film transistor connected to the first wiring, the second wiring, and the pixel, electrodes.
Preferably, the PVA liquid crystal display also comprises:
a second insulating substrate opposing the first insulating substrate;
red, green, and blue (R, G, B) color filters formed on the second insulating substrate;
common electrodes formed on the second insulating substrate and having a second opening pattern; and
a liquid crystal layer between the first insulating substrate and the second insulating substrate, wherein liquid crystal molecules are arranged perpendicularly to the first and the second substrates when no electric field is applied between the pixel electrodes and the common electrodes.
Preferably, the liquid crystal display also comprises pattern-formed a transparent electrodes. The transparent electrodes is preferably ITO (indium tin oxide), IZO (indium zinc oxide) electrodes etc. Also, the liquid crystal display preferably has different thicknesses by color where the red, green, and blue (R, G, B) color filters are located.